Backpack



FIG. 1 is a rear elevational view of a backpack showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a right side elevational view thereof;

FIG. 4 is a left side elevational view thereof; and,

FIG. 5 is an exploded view thereof.

The dash-dash broken lines illustrate stitching and portions of the backpack that form no part of the claimed design. 

CLAIM The ornamental design for a backpack, as shown and described. 